Inoculating loops have been used to transfer bacteria from one medium to another, e.g. from pathogenic substances to a culture medium. In the past, the inoculating loop has been a long thin piece of wire looped at one end. The loop was usually made of platinum wire and was sterilized by exposing the wire to a heat source such as a flame or an electric heater.
Because the heating process and subsequent cooling of the loop was somewhat time consuming, disposable plastic inoculating loops were developed and used. The inexpensive plastic loops were used once and discarded, avoiding the step of resterilizing the loop. The use of plastic loops accordingly resulted in a time savings especially when processing large numbers of samples. Additionally, because a flame or heating unit was no longer required, inoculations could be done in places which were previously impractical, such as in the field, under hoods, in anaerobic chambers, in glove boxes, in doctors'offices and for satellite laboratory testing. Safety was also improved in that accidental fires were prevented and spattering of pathogenic substances, caused by heating the substance in a flame, was avoided. One of the early plastic loops is illustrated in FIG. 1. As shown, the device is simply a long thin member having a loop formed at one end.
An improvement made to the plastic inoculating loop is shown in FIG. 2. This device again has a loop formed at one end. The other end, however, is needle-shaped and used as a picker. The picker is used to selectively transfer a bacterial colony to another culture medium for further growth.
The prior art inoculating loop may also be used as a streaker. A streaker is used to spread bacteria on a culture medium, such as agar in a petri dish. In practice, a loopful of material is placed near one edge of the medium or agar and smeared back and forth to make a small but thickly smeared area which can then be studied to ascertain bacterial growth.
Because bacterial growth may be too excessive in the specified smeared area, it is sometimes necessary to prepare a less thickly smeared area in the petri dish. This is done by making a single stroke through the thickly smeared area, carrying this fresh stroke of material to an unused portion of the agar in the petri dish, and then streaking that single stroke of material along the unused portion of the agar. This process can be repeated as necessary. One disadvantage in using the loop itself for streaking is that it should be resterilized or replaced after preparing each smeared area. A clean loop for streaking insures a clear separation of bacteria on the agar from one smeared area to the next. However, the necessity of a clean loop results in either time consuming sterilization or excessive waste of plastic loops.
One prior art device developed to overcome this problem is depicted in FIG. 3. In this device, one end is formed in a loop and the other end has a spherical shape. The sphere may be used as a streaker and is an improvement over simply using the loop itself to streak because it allows the user to streak with an additional clean surface by rotating the sphere to an unused portion of its outer surface. This results in more efficient use of a single inoculating device.
The use of a sphere for streaking, however, also has disadvantages in that it does not always provide the clear separation of inoculum/bacteria desired. There is also a chance of carry-over and contamination from one portion of the sphere to another. Additionally, it is often difficult to determine what portion of the sphere has already been used.
Although there are a number of disposable plastic inoculating devices on the market as evidenced in FIGS. 1-3, none is able to effectively perform the functions of transferring, streaking and picking the sampled material. More than one of the devices is necessary to satisfy those functions resulting in excessive disposal and consequent waste of the used devices. In addition, the prior art streakers are also inadequate. As noted above, when preparing multiple and progressively less smeared areas, a clean surface is desired on the streaker for preparing each new area. The loop or needle is not adequate for this purpose because each should be replaced after each smeared area is complete to prevent contamination of any newly smeared area. The sphere, although an improvement, is also not guaranteed to provide a fresh sterile surface for each new smeared area desired.